A method for removing persulfate interference in the analysis of the chemical oxygen demand in wastewater

Abstract

In recent years, sulfate radical-based advanced oxidation has received increasing attention for the treatment of water and wastewater. However, the chemical oxygen demand (COD), a common measure of gross organic contamination, is subject to interference from residual persulfate in the treated water. In this study, a new method, based on addition of sodium sulfite (Na2SO3) and heating, has been developed to eliminate the interference of remaining potassium persulfate (PSk) on COD analysis. Results of batch experiments show that potassium persulfate can be efficiently removed with molar ratio of Na2SO3/potassium persulfate ≥ 2 and heating at 90 °C for 60 min. This method (Na2SO3–heating treatment) was further tested in a phenol wastewater and a coal industry wastewater. The deviation of COD values of Na2SO3–heating treatment was lower than 5%, which was much lower than the deviation of the calibration curve method, of more than 14%. This new method could be applied to water samples containing persulfate and organic substances and help researchers to accurately evaluate performance of sulfate radical-based advanced oxidation processes.